The purpose of this study is to characterize functionally the regions of the H-2 complex by analyzing H-2 mutant mouse strains. The point or site of mutation will be mapped by genetic complementation, anti-sera analysis, a "lysostrip" technique, and blocking of activity in the mixed lymphocyte culture(MLC) and cell-mediated lympholysis (CML) test. Functional alterations in the mutants, compared to the strain from which they were derived, will be tested in MLC, CML and graft-versus-host reactivity. Further experiments will be done to determine if coculturing of the mutant and strain of the origin cells give rise to an allogeneic supernatant; and if so, an antigenic characterization of the active principle in the supernatant will be performed. The results of this study will, 1) locate the site of the mutation in these mutant strains to a particular gene or locus, 2) determine the antigenic alteration produced by the mutation and, 3) reveal what functional sequelae result from this change. This will lead to a further understanding of the organization and function of the different regions of the H-2 complex.